How Time Dilation Causes Gravity, and How Inertia Works
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- Опубликовано: 12 июн 2021
- The thing that’s pulling you towards the ground right now isn’t the force of gravity, as it’s commonly understood. Instead, you’re being pulled downward because that’s your natural path through spacetime, which is warped by the immense mass of the Earth. This warping primarily takes the form of time passing faster further away from the Earth. Spacetime warping in general also accounts for an object’s inertia and momentum, and we’ll get to that later in the video. How does spacetime warping result in the thing we usually call gravity?
Here's a donation link if you'd like to support my channel- many thanks! donorbox.org/idea-list-youtub...
By the way, at about 3:40 in the video I talk in terms of "hours" that the clocks are ticking off, and I should've clarified that the time difference between clocks a few hundred feet apart on the surface of the Earth is on the order of picoseconds, not hours! Misleading on my part, my apologies.
Here are the other videos I reference about how time dilation causes gravity. They’re really good, but the analogy of a “flow gradient” in time is nonphysical and, I think, just confuses the picture. I’d encourage you to give these a watch and decide which explanation makes the most sense to you: PBS Space Time: Does Time Cause Gravity?:
• Does Time Cause Gravity?
Science Asylum: The REAL source of Gravity might SURPRISE you...:
• The REAL source of Gra...
Physics Videos by Eugene Khutoryansky: Gravitational Time Dilation causes gravitational “attraction:
• Gravitational Time Dil...
Here’s a video that presents an excellent way to visualize four-dimensional spacetime warping: ScienceClic English: A new way to visualize General Relativity:
• A new way to visualize...
By the way, the animation at 10:43 was made by ScienceClic as well.
Here are excellent RUclips videos to explain each of the four assumptions we start the video with. There are many others that you can also find to supplement your understanding.
1. The three dimensions of space and the one dimension of time are inextricably linked into one dynamic medium: spacetime. TED-ed: The fundamentals of space-time: • The fundamentals of sp...
2. Mass warps spacetime in well-defined ways, and warped spacetime moves mass in well-defined ways. PBS Space Time: The True Nature of Matter and Mass: • The True Nature of Mat...
3. In the absence of external forces, masses follow geodesics in spacetime; that is, they follow the path of least local distance through spacetime. Veritasium: Why Gravity is NOT a Force: • Why Gravity is NOT a F...
4. Part of the warping of spacetime by mass involves time moving more slowly as you get spatially closer to the mass, so that for example clocks on the surface of the Earth tick more slowly than clocks on the international space station. (This is known as time dilation). PBS Space Time: How Does Gravity Warp the Flow of Time?: • How Does Gravity Warp ...
Late in the process of making this video, I found this paper published in 2017 in the European Journal of Physics by Stannard et. al. that gives quite a similar graphical explanation of objects following spacetime geodesics in curved spacetime: iopscience.iop.org/article/10.... It also has some additional analysis, including deriving a solution to Einstein’s Field Equations (that was published by Karl Schwarzchild in 1916) from the geometrical picture given. I can’t say that I was inspired by this paper in the making of this video, but finding it did quite reassure me that what I’m putting forward is correct! 
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The clearest explanation I have ever seen. I had the 'hang on - that's obvious when you say it like that' moment. More like this pretty please..
There is a point towards the end where you say, "There comes a point where the only way to increase the speed of the object is to turn the object into light." But, I believe a better way of saying that would be, "There comes a point where the only way to increase the speed of the object is to turn the object into something with no mass."
Good point! Agreed.
Yes, it's the ultimate trade-off! Either you are at "rest" with all motion through time, or have no mass so that all motion is through space (no time passes for you).
@@ALBINO1D
Song : "No time ( left for you [ luxons ] )" by "The Guess Who"
@@2hcobda2 Bot. Reported.
@@ALBINO1D for what?
Holy crap, I've had an amateur interest in relativity for 30 years but I've never understood gravity as a function of movement through spacetime like this before. Thanks so much, cool as hell.
I found Science Clic to be an amazing resource too. Similar descriptions: ruclips.net/video/wrwgIjBUYVc/видео.html ruclips.net/video/GQZ3R81iyE0/видео.html but there's a bunch of other videos there that are great. But I think this video indeed goes into even more detail.
I honestly think these are newer revelations. I too with 30 years of interest have never had it shown like videos these days now start to explain.
Indeed, this video is the best I found so far.
The presentation still left out issue of weight!!! He something are not very clear, but it should be accepted as their are till proof otherwise. Alright.
Because it's incorrect. Gravity is not a result of time dilation. This is a misinterpretation of correlating data.
Superbly explained.... Thanks for the effort and making things simpler to understand 👍😊
Great explanation, helped me a lot. Thank you very much for making this video!
This video answered questions that I hadn’t thought to ask. I really like your description of the “rate” at which mass warps and unwarps spacetime.
That's a great way to visualize it. Kudos on the explanation and illustrations. Very impressive.
I'm so impressed. This explains the equivalence principle. Movement due to gravity or normal acceleration impacts spacetime the same way.
Only the theory presented is supposed to do away with gravity as a force, as I understand it…
Also how is mass defined in the absence of gravity? As inertia? Sort of a resistance against acceleration?
It also seems to me that time would come out a space-vector - the path of least resistance between two locations in a three dimensional grid - which, to complicate matters further, is itself warped by all the masses in the vicinity in accordance with their masses.
Nevertheless, NASA must have precise, time proven methods by which to calculate these things. How else would they be able to slingshot objects around planetary bodies, as they often do? NASA can’t presumably rely on approximations, since last minute course-corrections would come too late, when their space probes is light-weeks away.
Couldn’t you start by covering how such calculations are done in real life before we let ourselves be overwhelmed by quantum conundrums?
Einstein described very well in the chapter "The Equality of Inertial and Gravitational Mass" of his popular book "Relativity: The Special and General Theory" the conundrum that experimentally it had been determined that inertial mass of an object is equal to its gravitational mass to a high degree of precision. Einstein's realization was that this equivalence might not be accidental. The fact that the gravitational "mass" exactly cancels out the inertial mass in the Newtonian equation for acceleration due to gravity indicates a purely geometric phenomenon behind gravitational acceleration. In other words, the "force" of gravity is fictitious, but the geometry is not what we thought it was.
@@IldarSagdejev I have the book and have read it a couple of times with great pleasure, so no!
That’s not what Einsteins says. He just states that there’s no way to discern gravitational acceleration from an equal acceleration by an equal force, unless you have some external reference, thus explaining why inertial mass and weighed mass must be one and the same.
The theory about distorting the space/time matrix came almost 20 years after Relativity was published and seems to treat time as a space-vector, which makes things more complicated to calculate, and as you know, a breakthrough usually means better and more generalized formulas.
But time, handled as a vector, must itself be distorted by mass, so how can NASA successfully calculate sling-shooting anyway?
@@Hallands.Interplanetary flight caculations use Newtonian gravity.
See "Mach's Theorem" for the possible nature of inertial mass.
The best video about this subject I have ever seen. It's also the first time that I have the feeling that I start to understand it.
Thanks for this.
I found your explanation much easier to follow that the video Space Time did on this same topic. 👍
It’s almost like mass creates a hole in space that space coagulates to patch/spackle - like a hole in the wall. And that greater density of coagulating space slows down time which results in geodesics whereby the slowest time is also the lowest-energy state that an object in a gravitational field defaults to.
The man, the myth, the legend himself! Thanks for watching, Tay. I like that analogy, I think of the formation of mass as basically just this, something like a knot tied into spacetime that pulls space inwards in all directions (at the speed of light), and which in some abstract way stretches out time as well.
atoms are mostly empty space. Matter does displace space, which pushes back against the matter as it passes through it. This causes a higher density region around the mass. Essentially, gravity is the effect of spatial pressure. We aren’t pulled towards the earth, we are pushed down onto it by space. So why time dilation? Time is just the rate of quantum vibration. In a high density special field, the vibration is slowed, ergo, time is slowed.
Oh wow it actually makes sense
@@lornenoland8098 define ‘quantum vibration’? How is that time?
E=MC2 is just a joke.., First off we live in a magnetic world. E=MD (Magnetic Density), All mater is magnetic all plants people everything we know exist is magnetic. The center of a magnet will prove all this to you!! Start working with the center of a magnet and you will see many things , Anti Gravity is one.. When Tesla tested his tower in Colorado for the first time he sent too much power from space into the local power plant and blew up one of the generators. FACT.. The north and south poles are the weakest part of a magnet, The energy in the middle once you learn how to use it will blow your mind!
best explanation of gravity I have seen so far
Agreed, this explanation is better than the other time gradient based explanations I've seen. Thanks for taking the time to make this video.
Yes, but humans can see movement over time, we can’t see warped space.
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Disagree.
This is very beautiful. It has helped me a lot. Thank you so much.
Thank you! That was a very helpful explanation.
Pure gold. Brilliant way to explain it. And now I FINALLY am beginning to get it. Thanks!!
Outstanding video and excellent narration. Your explanation is easy to follow and very clear.
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
@@Pastor_virtual_Robson Hmmm,.... and I love Derek from Veritasium. I'll look for his "original" version. thank you,
Simplicity is the key to understanding the notion of inertial reference frames and to understand euclidian space. Cool diagrams are important and you’ve nailed it here.
I loved your description of the attraction of matter to space-time causing gravity.😀😍 Resistance to movement change from forces and gravity and geodesics. The graphic was good to imagine matter sucking in space time. It helps give an intuition for it. Your questions give us ways to think about it and your answers frame it well, for sure! (Why does it take energy to move an object from its geodesic, ie an asteroid in space.)
Amazing, I've never seen it described like this! It makes so much sense to think of my inertia as me being attached to spacetime due to the way my mass warps it. Bravo
Yea that’s so believable, seems super logical, as long as you forget all knowledge ever known! Disregard everything ever felt, seen, heard, learned….-all sensible perceptions. Totally plausible! If that was no feat to overcome, then this wont be any brain-buster either…. Here soon the democrats will quit destroying the country, by funding good police and defund the wef, un, Soros, and their malnourished skinny Jeaned antifa creeps!
Wow! Thank you so much for making this and explaining it so clearly. Please post more
Glad you liked it! I would like to post more, but I've been busy with other things lately. Hopefully soon- do you have any topics in mind you would like to see explored?
@@IdeaListEye I previously visualized the warping of curvature as static around the mass, rather than as a dynamic/continuous motion of being sucked in. I’ve been ruminating on.. where this spacetime goes for lack of a better phrase. It just keeps getting sucked in? Maybe not enough for a whole video but the illustrations you used were so helpful to see in 3d vs the more common 2d depiction. I also think length contract doesn’t get as much love on youtube as time dilation, been trying to understand that better.
Mind-bending video ! 😉
I have been looking for this visual explanation for a while, and I was not satisfied with the videos you list in your introduction.
Now I know why it takes effort to climb up stairs!
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Wonderful and clear explanation. Thank you!!
I have spent so many pleasant hours thinking about this much like you have shown here. But the second part of it I hadn't thought about, more that I accepted that all objects follow the fastest path or the one of least resistance. Great video, thanks.
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Way better and more intuitive explanation than the referenced videos at the beginning 👏👏👏
This channel must rise up! This single video filled many gaps that I've been thinking about, even after all that very same great references (PBS, Eugene, Asylum and ScienceClic). I found it searching "gravity and entropy", and I hope I can find something about it around here. Thank you!
Thanks, Gino! I'm glad you found it helpful, that's exactly what I was hoping for in making this video.
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Thank You so much for this video. This is the first video I have discovered so far that explains the reason of falling of objects in a proper way. 🙃👍
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Beautiful, it shows a dynamic space product of the energetic presence (see the previous comment for the quantum approach), so gravity potential energy is equivalent to the kinetic energy of speed √[2GM/R], Schwarzschild time dilation is equivalent exact to Lorentz dilation. The relativistic view is the union of observable speed plus the equivalent gravitational speed! This and more can be read in a small amazon book "Space, main actor of quantum and relativistic theories". Thanks for your great videos
i finally got it with your apple example. thank you.
Wow! I was never satisfied with the time gradient. Thanks a lot
I dont think any better video of explanation of Spacetime is available on internet. Its awesome. Very well and simplistically explained. Would like to see such videos on quantum mechanics too if by any chance u prefer to make. Thanks a lot
Thanks! Would love to make more physics-y videos, hopefully when I can find the time.
The best explanation of how time dilation is a symptom of warped spacetime which itself causes gravity (i.e. why objects accelerate towards the earth. Thank you so much as have been trying to get for over a year now 😄
Really liked this explanation. Thanks!
This is probably the cleanest explanation I've seen in any medium. Bravo! (I had two GR courses in grad school. I've read most of the graduate-level GR textbooks, and read fairly recent research papers...and Kip Thorne's office is a few minute walk from mine). I would just point out that energy is the thing that causes time dilation somehow (energy density, more specifically). Mass just happens to be a compact form of energy. The deep connection between energy and time might be a hint pointing us toward understanding why energy density slows time.
Huge thanks, Dr. Stickley! Very much appreciated coming from you. Re. “The deep connection between energy and time might be a hint pointing us toward understanding why energy density slows time”, I’ve been playing around with the idea that spacetime warping is due to the density of particle interaction in a given region of spacetime alongside the need for relative positions and momenta needing to maintain a relativistic relationship to the speed of light. In other words, mass could be thought of as an emergent property (due to spacetime warping) that arises out of the interaction of e.g. fermions and bosons, and is not itself a fundamental property that particles (or energy) have. In simple terms, the more boson/fermion interactions, the more spacetime needs to be “knit” by those interactions into a web that maintains relative positions and momenta relative to the speed of light always being constant. The seed of this idea is the observation/hypothesis that only some interaction can define a particle’s location and trajectory in spacetime; absent these interactions, the particle exists as a spread-out “impulse” in the quantum fields, quantified in our framework by its probability amplitude.
I dug a little into particle physics to flesh this intuitive idea out and learned that I’m way out of my depth there. Something I’ll probably continue pondering, though.
@@IdeaListEye The current standard explanation for what creates mass is the Higgs mechanism; things acquire mass by interacting with the Higgs field, but this interaction is only responsible for a small part of a particle's mass; it's enough to keep the particle from moving around at c like a massless particle, but most of the measured mass of a particle comes from field energy (i.e., the swarm of virtual particles) around the particle. For an electron, most of the mass is due to energy in the electromagnetic field, since electrons have electric charge which binds to the electromagnetic field; for a quark, the mass is mostly due to the energy in the gluon field, since quarks have color charge which binds to the gluon field. The mass of composite particles, like protons is mostly due to the kinetic energy of the quarks it contains, plus the energy stored the gluon field and electromagnetic field.
Some people think that inertia may be due to the Unruh effect. I've been in favor of that general view since high school. This seems pretty similar to what you've been thinking about. Do a Google search for "is inertia due to the unruh effect?" to find out more.
I've also been playing with the idea that the rate of time passage in a region of space is somehow inversely related to the density of interactions in that region of space. I haven't been able to flesh it out into an actual theory, though. If it can be done, then gravity emerges as a direct consequence, so it would be a big deal.
You might also find "loop quantum gravity" to be interesting....there are some interesting ideas there, even if it doesn't turn out to be the way nature works.
The spokes on a wheel grid analogy were fantastic. Thanks
I was commenting on a video just yesterday on how the warped 2d net in so many videos give you an incorrect picture of what is actually happening, since the warpage of spacetime would take pace in all directions at once. I give you credit for showing this warpage in a more true to life model. Thanks!
Thanks! I'd like to add that the visualization at 10:43 is by the channel ScienceClic, I neglected to include a credit there (my bad!). (Their channel is superb)
Finally, I’ve been trying to understand the curvature of space time for a very long time and this explanation is beautiful, this is just so amazing to me and the fact that Einstein figured all of this out on his own is amazing to me. Best explanation I’ve seen, I finally understand, thank you so much. This is so cool and it is such an amazing way to think about gravity
Einstein's work here was absolutely astounding, but he didn't do it alone! The work of his advisor, Hermann Minkowski, and the work of Lorentz were indispensable in his development of special and general relativity.
This video should be included in the physics courses they teach in school. The best explanation of gravity on the internet.
Thanks for an illuminating video. I find this topic endlessly fascinating. Your explanation adds to my understanding and for that I am grateful. You simply can't do enough on this topic. More please!
I'll have a look at your other videos.
Remarkable work. Thank you.
According to Dialeckt's channel, time dilation is NOT the cause of gravity and Eugene Khotorkansky, PBS Spacetime, Nick Lucid are ALL wrong.
What is offered in this video is a different description than the usual one. This is due to your starting question: what causes gravity? Answer: time dilation. And this video does a fine job in answering that question. The usual starting question from a historical perspective was: what causes time dilation? Answer: gravity. Each of these descriptions are equivalent. And that was the genius of Albert Einstein.
way better and makes no room for arguments than Asylum
Hello. Thank you for that great video. It makes things very clear. I was nevertheless wondering why the trajectory you draw through spacetime is a portion of circle. Would n't has to be parabolic ? Or i miss something. (Which is certainly the case).
Phenomenal video.
I 've been thinking why it is so difficult to understand these notions, and came to the conclusion that the problem is not only due to our experiences, the problem is also verbal. There are no words to describe situations that fall away from our experiences and senses, which is exactly what relativity theory is doing. OR ARE THERE? Plato (and Freud in is own words) say that simple statements (words) require deep understanding. I understood what the narrator is trying to commune when I realised that all objects near a big mass (like earth) have the same ANGULAR SPEED (two words) on the space time diagram. These two words crystalized the meaning of the theory and helped me remember all the details effortless.
Awesome approach! I love finding new teachers like you. Keep it up
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
@@Pastor_virtual_Robson I wrote this comment on a completely different video, not Derek's either. Weird
this is the best video ive seen and it has cleared my concepts to another level. keep doing this . also share your donation link.
Thanks, SpacetimeGrid! I was having a bit of a rough day, it's really nice to hear that kind feedback, just the pick-me-up I needed! Thanks also for your idea about a donation link, I had been thinking about making one for awhile and you gave me the push I needed. Here's the link, many thanks for your support! donorbox.org/idea-list-youtube-channel
Great video, thank you... just a question though... according to equivalence principle, an object in free fall is like a floating object moving freely through its geodesic in spacetime (like the space station)... so according to my understanding, time for the falling apple should be as fast as it is for the space station until it falls on earth, at which its time will move slower... am I missing something?
Interesting perspective on GR and inertia. Thanks
Tanks you . Please do not stop making such vidéo.
Excellent video, thanks!
You attempted to be clear and intuitive in detail at both your space and our time, the graph puzzle links a solution, IF those historical theories where snapped together as one. Allowing a healthy questioning, without any rightous declared says. We don't get much *mass* explanations, from those other channels you mentioned on this one.
Love this explaination❤
given that the speed of causality, or the propagation of spacetime warping is the speed of light, your explanation or warping and unwarping as mass travels makes it intuitive to understand why nothing with mass can travel faster than the speed of light, as it would create a "sonic boom" of sorts, i.e. tearing spacetime.
Cool observation! I hadn't thought of it like that, but I see what you mean.
Best explanation ever! I mean it. Can I make a request? In GR peoplw say spacetime has mechanical properties all its own, in this video you referred to spacetime's resistance to being warped. Can you explain a little about this? It seems very different from classical empty space!
Thank you! Happy to talk about this, fascinating question. In general, in light of GR and quantum field theory, it's wrong to think of spacetime as "nothingness", or "empty". Spacetime is a substance with well-defined properties (including a relationship to matter mediated through gravity). Nailing down the details of those properties is tricky; would it be right to say that everything is fundamentally made of the same substance, and that particles are just particular "conditions" placed on a given region of spacetime? Some would say yes (string theoreticians for example), some would say no. Those kinds of finer points are beyond our knowledge at this point.
@IdeaListEye Yeah! Beyond our knowledge! Please make a video about it! Thanks again.
So this is the way to think about uniting the forces into one grand theory. So simple and elegant. Just as scientists envisioned since the Greeks. Bravo!
Excellent explanation of how gravity works. Much better than the three videos you mentioned in the beginning. I would love it if you expanded your examples of traveling through the geodesics to objects flying by a planet at different speeds. Explaining why speed matters and why traveling at different speeds determine the geodesic path of the object. At high speeds its path is slightly bent. At the right speed it winds up in orbit. At lower speeds it crashes into the planet.
Thanks! And agreed, that would be a useful illustration of how geodesics are tied to momentum.
@@IdeaListEye pls make this. there is very little research on the relation between inertial forces and geodesics.
Just 86k views?? This video deserves to be one of the best science videos I've ever seen, so much information in such a short time, and very well and easily explained as well. You are great sir.
One request for u, please explain delayed choice and delayed choice quantum eraser and other quantum related ideas sir since you'll be able to explain them simply as well I'm sure 🙂❤️❤️❤️
Sabine Hossenfelder did a great video on the subject recently. Basically, you need to combine the interference pattern from both detectors when interpreting the result. You can’t just show the pattern from one detector which a lot of other videos do.
@@eyesopencam Thanks bro, I'll look through it 🙂❤️
Wow, thanks, Umer! Very kind of you to say. I'd like to dig into those topics, thanks for the request. I have been reading about quantum computing recently, and it's monumentally complicated and confusing-- it might be a long time before I have anything valuable to say, but stay tuned!
@@IdeaListEye will be waiting sir no matter how long 🙂
No, because it is wrong, very wrong!
omg this was a brilliant video i really understood this wow i can see why so many see the beauty in GR.
very interesting video. i always used to think of time as if it itself was flowing rather than matter travelling in the spacetime continuam
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Thanks for creating and posting this awesome video! I could never understand why an object released from a stationary position (like a tree branch) in a gravitational field would start moving if there is no force involved. What would give it the impetus to start moving? Now that I've seen your two-dimensional graph of warped space-time, I finally think I understand it. If I understand this correctly, the object is fixed on a geodesic position, but the geodesic fabric is changing with respect to time, thus causing the object to move through the space dimension. i hope that's more or less correct anyway.
Hey David, you're welcome! Glad it helped you out.
Re. "If I understand this correctly, the object is fixed on a geodesic position, but the geodesic fabric is changing with respect to time, thus causing the object to move through the space dimension."
I think that is more or less correct, but a better way to think about it would be to say that the object is fixed on a geodesic path, not position, because every object is always traveling through spacetime; there's no fixed position because even if it's somehow perfectly stationary in space, the object is still traveling forward through time.
Using the apple as an example, the geodesic path the apple seeks to take (its path of least energy through spacetime) has it traveling downwards due to the curvature of spacetime making every other path require more energy. It's only kept from following that path by the branch exerting a force on it away from that path (upwards). So, to be clear, it's not that the "geodesic fabric is changing with respect to time"; that geodesic is fixed by the interaction between the Earth's mass, the apple's mass, and spacetime. When attached to the branch, at every instant the apple is traveling further through spacetime than it would if it could follow its preferred downwards path because the branch is pulling it away from that path into a region where time passes more quickly (causing the apple to travel through more time than it would if it were in free fall along its geodesic). I hope that helps! Let me know if you have any questions.
@@IdeaListEye Thanks for clarifying that. I see what you mean by the object not being "fixed" on the geodesic. It is always moving through time. I hope I've got that correct now. I also think I see what you mean when you say the geodesic is fixed, not the object.
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MUY buen video.
Utmost didactic. THANK you ❗
Despite beeing an engineer, my understanding is still a bit nebulous.
But my intuition tells me that I am going to understand it way more intuitively now, more naturaly 👍.
Now, I can grasp at least, that the traditional way of learning/explaining gravity as a force, as an "attraction", is simply wrong 🤔.
Literally, what I learned here makes me feel lighter, enlightened.
Your video is really great ‼️‼️‼️
Saludos de
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Great Explanation .
Very very nicely done! Thanks.
Thank you so much for this. I was screaming at the screen while viewing the other videos you mentioned because of their darn time-flow vector that didn't seem to have anything do with spacetime (or just space). If felt like a relativistic three-card monte. So well done.
But you've given me something new that just feels wrong (not saying it is, I'm just having trouble accepting it): If it takes extra energy to warp spacetime to get the asteroid to move over, (and this makes perfect sense), once it's up to speed it will keep going with no new energy added (at least no new external energy). But the asteroid is still warping spacetime anew as it moves along. That feels like this warping and unwarping should need energy too, just like it did to get the asteroid out of the well it had formed at rest. Or at the very least, the motion would run down as energy gets used up, and of course this doesn't happen.
The direction of travel length contraction item seemed a little shoe horned in there (bare with me here, this is not meant as a critique). So I wondered if the length contraction has something to do with the asteroid being "attracted" to the spacetime it is about to move into and warp, and I just missed that connection. Or is there a length contraction gradient which would translate to a mass gradient would translate to a time gradient and we're back to what causes gravity but this time, in direction of travel; once an object is moving, or once spacetime is unwarping, does the object create its own "straight" geodesic?
That the asteroid is "attracted" to the spacetime it is about to move into (in this example), feels similar to why mass (or probably better: energy) causes a dent in spacetime. I'm hoping the answer is not "because it does" as it currently is for why mass dents spacetime.
It also feels a little like something riding a wave. The displaced spacetime behind pushes the asteroid forward - but there is an equal ridge of spacetime in front that must be overcome, so the energy supplied to ride down the hill would be the same as the energy to climb the hill in front. (unless due to motion there is now a time gradient so there is a lag between when the energy is supplied and needed.) Or is it that spacetime itself has inertia?
Again, thank you, I've been chasing the "time causes gravity" for some time now and the veil has been lifted.
Thanks! And thank you for these insightful comments, I was hoping someone would raise some of these issues.
"If it takes extra energy to warp spacetime to get the asteroid to move over, (and this makes perfect sense), once it's up to speed it will keep going with no new energy added (at least no new external energy). But the asteroid is still warping spacetime anew as it moves along. That feels like this warping and unwarping should need energy too, just like it did to get the asteroid out of the well it had formed at rest."
This is a great question. To clarify the picture, it's better to say that it takes extra energy to change the rate at which the asteroid warps spacetime, not just that it takes energy to warp spacetime. When you speed up the asteroid in the x direction, the asteroid now needs to warp more space per time in the forward x direction, and unwarp more space per time in the backwards x direction. Because mass is attracted to spacetime, the object moving through more spacetime in the x direction is more strongly attracted to spacetime in the x direction. By the same token, the object moving away from more spacetime in the backwards x direction is more strongly attracted to spacetime in the backwards x direction; the influence of the extra warping in the forward x direction and the extra unwarping in the backwards x direction cancel out, leading to a constant velocity. This is the case in any inertial frame (even for a hypothetical object that's completely still in space), the object's attraction to spacetime in every direction cancels out, leaving the object moving at a constant velocity. It takes extra energy to upset this equilibrium by causing the object to warp/unwarp extra spacetime in any direction (which results in that object picking up velocity in that direction).
One way to say this would be that the extra attraction that the mass gains to the more rapidly approaching spacetime in the forward direction is "paid for" by an extra "drag" on the mass by the more rapidly receding spacetime (which is also attracted to and attracts the mass) in the reverse direction.
I like your idea of an object moving through spacetime as similar to something riding a wave, but I disagree with the way you have it stated ("The displaced spacetime behind pushes the asteroid forward - but there is an equal ridge of spacetime in front that must be overcome, so the energy supplied to ride down the hill would be the same as the energy to climb the hill in front."). Try to imagine this wave instead like an attractive field, maybe like a magnetic field. The approaching spacetime attracts the object forward, and the receding spacetime attracts the object backwards, and the two cancel out (for any constant velocity in the absence of other forces). The thing that applying a forward force does is cause the object to be attracted to more spacetime in both the forward and backward directions per time (and thereby to travel more distance in the forward direction per time).
You're right that the bit about length contraction was a bit shoehorned in; I included it in the video because length contraction and time dilation are correlated with increased velocity through spacetime, but not because that fact gives useful explanatory value in the case we're discussing. The space contraction and time dilation that occurs for objects moving relatively faster than others can be understood better in the context of light clocks (I'll assume you're familiar, let me know if you'd like any clarification). For a light clock traveling through space faster relative to another light clock, the photons must travel farther to tick off the same amount of time (resulting in time dilation), and space also contracts in the direction of motion to accommodate this effect. This is true not just for clocks, but for all physics: in order for the equivalence principle to hold, for an experimenter traveling at 99% the speed of light, the photons involved in the electrical currents in the experimenter's neurons, in the biochemical reactions keeping them alive, and in lighting their experiments would need to travel a ludicrously long distance in the forward direction if space contraction in that direction didn't compensate (alongside time dilation). Kinetic time dilation and space contraction are required to allow objects moving near the speed of light experience the same laws of physics that objects moving at 0 speed follow.
@@IdeaListEye Thanks for the in depth response and for the respectful tone (so many of these presenters get down right nasty when you ask something) I'd like to solve time travel just to go back before they knew these ideas and give them a taste. There was always a time before we all knew.
Anyway: The befuddlement around the inertia section comes from the warped spacetime resisting being unwarped and needing energy to do that. So far so good. But then one the unbalanced force is removed the asteroid continues to anger spacetime as it unwarps the space it is in and warps the space in front, and to my thinking, the asteroid would have to expend its kinetic energy to keep that up; the warpage acting kind of like friction. Why is a body in motion more slippery than a body at rest? (with respect to the spacetime it warps)
Regarding mass's attractiveness to spacetime, based on the inflow 3D representation of this it seems like that flow would empty the universe in short order. Is this the correct way to think of it? Is this better than the idea that mass just warps spacetime instead making a sink? (so a still from that animation instead of a constant flow?) Is it a flow or a stretch?
Assuming a spheroid asteroid of even mass distribution, time dilations would be consistent all the way round, spacetime warping would be the same all the way round, I'm having trouble understanding why spacetime would being willing to unwarp and warp in the direction of travel with no added energy since it took energy to to do it in the first place from rest.
Or is it better to look at it this way:
From a geodesic point of view, instead of saying it takes energy to unwarp the space, would it be better to say it takes energy to alter the geodesic? (I think you kind of said that) For the at-rest sphere, the geodesic is as you depicted. With a push, we are angling it's geodesic over a little bit (I think) where it stays once the push is removed. On this new geodesic it's free to continue on its merry way because that is the lowest possible energy state and it's warping spacetime as it goes because, well, that's what mass does inherently. (BTW, to be clear, it's not that I doubt this happens, it's the depiction that energy is required to unwarp and warp space anew that has me frowning) As you say, if inertia is still a shoulder-shrugger even for Kip Thorne et al then there may be no answer to this.
Whether the sphere is warping spacetime while it moves or is stationary probably doesn't matter - the energy to do that is built into the mass of the object doing the warping. Does the motion really matter at all? Spacetime is reacting to the proximity of a bundle of energy and I"m not sure that needs any help or incurs an energy debt.
I love your geodesics diagrams for time causing gravity. I have now found another video that finally visualizes time and length contractions and dilations by warping the graph grid itself with the lorentz tranforms, while the spacetime motion remains the same - light bulb moment! (I prefer to get the concept before digging into the math - I came form the shut up and calculate school - I get the right answers when doing the math but I'm queasy about why. I could be wrong on this but I think Einstein made bigger leaps in the field by conceptualizing than in doing the math)
Yep savvy with light clocks. I was just thinking perhaps length contraction had something to do with how the object would be attracted to spacetime (bit of a hail mary on my part) and thought that's why that segment was there. Can't-get-puzzle-peice-to-fit!
@@markrichards5630 _"But then one the unbalanced force is removed the asteroid continues to anger spacetime as it unwarps the space it is in and warps the space in front, and to my thinking, the asteroid would have to expend its kinetic energy to keep that up; the warpage acting kind of like friction."_
The thing that "angers spacetime" (lol) is not the fact of the extra spacetime warping, it's a change to the _rate_ of spacetime warping. This is why an object way out in space resists acceleration proportional to its mass, but moves at a constant velocity (no matter how fast, up to the speed of light) in the absence of other forces. Spacetime warping at any _constant_ rate offers no resistance to motion (so it's wrong to think of it as like friction). The thing that is "frictional" is changing the _rate_ at which an object warps spacetime (which corresponds to changing the object's velocity through spacetime, i.e., accelerating it). Once you remove the unbalanced force, you're no longer changing the rate at which the object is warping spacetime, and the object/spacetime happily continue on in their new, faster interaction.
_"Regarding mass's attractiveness to spacetime, based on the inflow 3D representation of this it seems like that flow would empty the universe in short order."_
I borrowed that video representation from a great youtube video, ruclips.net/video/wrwgIjBUYVc/видео.html. Be careful in your reading of it- it's an attempt to show both space _and_ time simultaneously, and it's not showing space warping as time passes; it's instead showing inertial spacetime frames (and is a bit of a confusing picture because of that). The warping of a mass at rest far out in space is constant, and the warping of time by that mass is also constant, so there's no inflow of spacetime. The inflow applies to other masses embedded in spacetime whose geodesics have been directed by the first mass's spacetime warp towards that first mass.
_"Whether the sphere is warping spacetime while it moves or is stationary probably doesn't matter - the energy to do that is built into the mass of the object doing the warping. Does the motion really matter at all?"_
The motion definitely matters, and the nature of the sphere's warping of spacetime while it moves or is stationary _defines_ that sphere's motion (in particular, its momentum). If you believe in the conservation of momentum, the motion definitely matters. Specifically, the rate at which spacetime is warped by a moving mass (with that rate highest in its direction of motion) _is equivalent to_ that mass's momentum.
@@IdeaListEye Thanks for taking the time. This makes sense now - any disturbing of a motionless object or a constantly moving object would be an acceleration and therefor you can either look at it as that energy is needed to change the rate of motion or change the rate of warping. For my noggin I think I like the idea that the energy used to change the object's motion is in fact changing its geodesic. Is this a reasonable way to look at it? Ignoring relativistic speeds, is it safe to say that because the mass of the object doesn't change, the local shape of the curve it produces in spacetime doesn't change, and the geodesic just moves over, or, does the angle of the geodesic change too at the new constant speed?
I love how spell check turns a mangled "geodesic" into "videodisc" - I guess that's the flat-earther solution to this problem)
@@markrichards5630 That's right, the energy used to change the object's motion is changing its geodesic. This is how satellites stay in orbit: by putting in the right momentum, they now travel along a geodesic more or less parallel to the surface of the Earth.
Excellent explanation👍
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Cheers!!!, I finally found an explanation that an old engineer can understand 👍🙏🙏
The casimir effect is probably related to why mass warps spacetime, I tried making a very simple abstract model of it (probably terrible way to go about it) but it would make sense, an empty region of space exerts a certain amount of force, the force pushes equally on other empty space and it cancels out giving flat curvature, as soon as any mass occupies it, it "blocks out" the things the effect emerges from and the force is no longer fully balanced out on neighboring regions of spacetime.
like there is something that props up spacetime so it is flat, like if you had a trampoline with the skin of it levitated by something that is "obsured" by mass
It is funny that you think the purpose of the video is to simplify what others failed to explain regarding spacetime. 😋u actually made it even harder to understand😘
These might be the best explanations I've seen of these topics!
We love this video! You’re right that the connection between time dilation and gravity is only made more confusing by the “gradient flow” analogies of other videos. And we like that you’re not afraid to tackle the big questions - “why does mass warp spacetime” is the essential mystery left behind in the wake of GR. Interesting to think, for instance, that an accelerating object, in consequence of the equivalence principle, must observe a gravitational field, i.e. warped spacetime, in the vicinity of itself, and that the strength of this field is independent of both its mass and velocity.
Great work, we look forward to your future videos!
Many thanks! I hadn't heard of your channel before, but there are some really interesting topics there; looking forward to checking them out.
@@IdeaListEye Hah, we’re not big, but hit us up anytime!
"... an accelerating object, in consequence of the equivalence principle, must observe a gravitational field, i.e. warped spacetime, in the vicinity of itself, and that the strength of this field is independent of both its mass and velocity."
Well, lets do some philosophy. The only two entities in your statement that pretend to be real are the accelerating object and the act of observation of some object which is different, i.e. on the outside, from this observing and accelerating object. In this case, one may say that the observed object is the exterior, should we say the outside, of observing object. However, according to GR equivalence principle nither the accelerating object nor the gravitational field are real, therefore "the strength of this field is independent of both mass and velocity". Actually the only two real entities in your statement are the change of the rate of change, which is real because of it"s actual limit /the speed of light/ and the continuity of the extension /or the duration/. Just forget about the force and strength.
I have always taken the views that a) spacetime emanates from every point in all directions, thus allowing for changes of direction and time and b) nucleons, which to me are almost condensed parts of spacetime with rest mass, warp it because they are impermeable and so spacetime cannot go through them, spacetime almost concertina’s up around them. Bearing in mind most solids are vacuum and when mass is really concentrated then their mass such as a black hole completely blocks spacetime as opposed to Earth which only blocks enough for us to weigh what we do at the surface. Would love to develop this further.
The constant emanation is probably what we call the dark force. The emanation is what non mass waves ride along, at the speed of c. So mass is to me proportional to the volume of spacetime it encapsulates.
I've had a life long obsession with this subject and have come to the same conclusion that you have. Your video however has deburred the rough edges of my thinking and really brings the idea into focus, in a way that, so far as I know, is unmatched. My only disappointment is that you didn't illustrate the mechanism in which mass causes this effect in spacetime but my forgiveness is gratuitous, being that it's a very difficult problem to solve.
@@GriuGriu64 I think its useful
Thank you so much..
Great explanation! Certainly regarding inertia.!
But do the rules apply when you have a black hole as mass (instead of the earth) and an apple that falls from the branch towards the black hole...?
At one point the apple will be going 99,9999999% of the speed of light and weigh as much as a small planet (and thus even will fall faster, not?) So there has to be a factor in the equation that takes this into account. That objects, as they fall , gain mass. Or am i wrong?
Excellent video! I think I understand this concept much better than before! Hope to see more videos like this! Thanks!
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
I have a question related to the video and the equivalence principle. It seems a logical conclusion (to me, at least!) that from the equivalence principle we could potentially try to re-derive kinematics in terms of time-differentials. In other words, we can look, for example, at acceleration as applying a time-differential across the accelerated object. Another example can be the interpretation of constant velocity that can be described as a constant time-flow differential across the two reference frames. If that holds, could we define the concept of inertia as a measure of the propagation of the time-differential field...? Could geodesics be defined via a temporal-related description? Could a temporal version of F=ma be defined? It would be really interesting to know if any work been done to explore this path... sort of time-differential kinematics...(I just made up a name... :D) ? If so, are there interesting (positive or negative) results from previous research?
Great video!
I can't believe this only has 250k views. This deserves to be seen. Top content
I think Einstein's work is very straight forward in the sense of how the time causes that things fall down. Any way, i think your work is great.
Great explanation, that helped me visualize it alot better
"because things pass through time at different speeds at different elevations. " I have watched HOURS of gravity RUclips videos to finally find this sentence. THANK YOU!
One thing I wished you had explained regards the stumbling block I had when I first tried to understand time dilation. I could not get my mind around the fact that two old school mechanical clocks would show different times when one was moved away from the earth. It seemed like they made a mistake as the mechanical mechanism should give the same result. The glossing over the reason this happens at an atomic level is not usually explained and causes a headache when trying to put the whole picture together. Maybe a topic for a future video? André in Sydney
This has been a consideration from the start, and a lot of very smart people have taken great pains to address it (and to test what you proposed, whether it's just a mechanical accident or actually a consequence of fundamental physics). You can read more here: en.wikipedia.org/wiki/Experimental_testing_of_time_dilation
Great ideas! 👏👏
I know how/why matter warps space around itself, and creates an inverse square gravity field and a "circular" GTD field, at right angles, and yes the GTD field may also affect gravity, but I'm still not sure if it's pro or anti' gravity!? But I am still trying to understand what causes VDT and length contraction, in the direction of motion. They must all be connected, somehow. And what about the relativistic mass gain/inertia? Does it also cause g? I just figured it out, and the 2 effects go together, of course.
Thanks so much
The curve you describe makes me think of a record player. The centre and the outer points seem to make one revolution at the same time but the outer edge point has a larger diameter and so moves faster through space time. Would this be an apt analogy? Great vid nice simple chunks to help a person learn the more complicated parts in the future. Take care keep well.
Hi Vincent, interesting comment. I think it's not exactly an apt analogy, because all objects always move at the same rate through spacetime (at the speed of light, which is a confusing point in itself, but I think this video's description contains a link to a good video that explains this). The thing that changes from point to point in space relative to other objects in space is whether that thing is traveling at the speed of light solely through time (i.e. not moving relative to those other objects) or having a component of its travel through a direction in space (while traveling less than the speed of light through time as a consequence).
@@IdeaListEye Cheers mate I knew I wasn't there completely with that analogy lol or at all. This will help no end, much appreciated. Thanks again and all the best, take care.
Thanks for this video. With such a grip on spacetime and matter/energy, you should take the next step into fleshing out how entropy and enthalpy further quantize the events of causality. Essentially, what I’m asking you to do is to connect relativistic mechanics to quantum mechanics via focusing on entropy/enthalpy and how they define the arrow of time (or as I put it, further quantize causality).
Neither the standard model nor relativity make enough sense to fully model the world without each other, which is why Einstein spent most his life seeking the bridge and it remains the holy grail of physics. From what I understand about relativity, to consider gravity/time a force mediated by spin-2 tensor bosons is… unintuitive, while to a particle physicist, it is intuitive to consider gravity/time a fundamental force mediated by force carrier particles, as included in most standard models.
It’s literally looking for a fundamental particle for time, which imo is like looking for fundamental force carriers for speed, momentum, or inertia. These all seem like composite, non-fundamental forces for which there wouldn’t be a bosonic force carrier. It seems to me like we already have all the fundamental particles we need, what we are missing is a better understanding of how they interact via enthalpy and realize entropy. That’s so far quantifiable via high level quantum mechanics that can model up to a sufficiently composite, classical degree.
Furthermore, I would interested to see if the right understanding of the connection between quantum mechanics and relativity via entropy/enthalpy could also shed a bright light on dark matter and more importantly dark energy.
Cheers, pls do this for me even if you manage to prove this all wrong
Hey JackBlackNinja, thanks for this suggestion. It's an interesting idea, but I'm not particularly qualified to confirm or deny it. I'd encourage you to flesh it out, and perhaps even make a video on your own to explore and express your idea! If you were interested in doing so and had questions, I'd be happy to help in that regard (re. video production, etc.).
@@IdeaListEye I would so much like to make a video myself but I feel like I don't have the physics prowess nor editing skills to pull it off. You did so well with this video, which itself deals with time, so was just thinkin you might be able to explore the so-called 'arrow of time' described by the 2nd law of thermodynamics, which is a macro composite of quantum phenomena called micro states. This connection between the arrow of time described by the quantum mechanics via the 2nd law and the gravity-time described by relativity seems interesting to explore. Anyway, I totally understand if it's out of your wheel house, it's certainly out of mine too!
Keep up the stellar work boss
Timestamp (10:02) "...Inextricably..." I am awed at how mystical it sounds but for the life of me I cannot wrap my brains around it. Even more mid-boggling and stunning is this exoteric 'Spacetime'. Do you have anything oh say Heat-Velocity, or Ampere-Moll, maybe even an Ampere-expansion phenomenon? What in the world is the definition of a dynamic medium? Thank you in advance.
Thank you for pointing out that there is no generally agreed upon theory for why inertia exists. I have been trying to find the answer to that question for years and no one else has simply said that "we don't know". They always just talk around the subject. I have watched pbs space time, dr lemon, and many others. Arvin an gets closer than most, but only you have just come out and said it.
Awesomeness video!
Great Video. I love your perspective. I did not like the Science Asylum's version, although sometimes my mouth does act faster than my feet!
the video belongs to another youtube channel Veritasium ... that channel just stole the video.
Excellent video, which finally explains gravity through space-time geodesics in curved space-time. Was always left confused by the other videos mentioned. Thanks for this comprehensive video!
Also, I wonder whether you can create a supplementary video explaining the math of the field equation using a single dimension for space and time, like you have done in this video? You can also eliminate the factor for the expansion of the universe from the equation.
Hi Ravi, thanks for your kind words! I most likely won't be able to find time to make a supplementary video for this in the near future, though I agree that would be interesting. This paper might help clarify how this viewpoint relates to the field equation: iopscience.iop.org/article/10.1088/0143-0807/38/1/015603
Good video.
Is warped spacetime the displacement of the fabric of the universe? Causing this fabric to be "squeezed" and in multiples around the object?
Because the universe is constantly expanding, and now that we have multiples of this fabric, does this cause tume dilation and gravity?
This fabric would be most abundant at the surface, and the further out you are the less of this fabric there is.
Nice video. Very much appreciated. But @13:15, is it that time dilation warps spacetime geodesics towards the Earth's center of mass or is it the earth's center of mass which determines the shape of these geodesics? This was stated as the main point of the video, but not enough time was spent explaining the difference between these two statements, if there is one.
Thanks! Good question. Even though this video sets out to show that the gravity we experience on earth is caused by time dilation, what I’m really trying to get across is that both are one and the same. That is, the thing we call gravity, which is the force we feel pulling us downward, is equivalent to the effect that time dilation has on the path our bodies seek to follow through spacetime. It’s not the case that one causes the other; they’re the same thing, and that single phenomenon is the result of the way mass and spacetime interact.
This is one of the best and clearest explanations of how the gradient of slowed time causes the gravitational "pull" toward the center of a body of mass. Since you are obviously a great teacher, I would like to ask a different question
I accept the premise that the gradient of time causes the gravitational effect, and that concentrated energy is the source of this gradient, whether in "pure" form or packaged into mass. My question is HOW does that energy create the gradient of time around it? I have not found anything the provides even an attempt at explaining that
A related question is that we know that the time of all parts of a moving object slows down as seen by an outside observer. What happens to the space around that object? Is there a sudden jump, or discontinuity in time between the border of the moving object and the space around it? Or does it create a well where there is a gradient of slowed to "normal" time as you move away from the object?
Tying the two questions together, could the gravitational effect of a mass be caused by all that energy basically moving at the speed of light - but of course trapped within quarks and other subatomic particles - and the net effect creates a well of depressed time that extends beyond the boundaries of the mass, which then becomes the source of gravity?
Thanks! These are very interesting questions. Let’s call them questions 1, 2, and 3. Question 1 (“HOW does energy create a gradient of time around it?”) is similar to asking “how does an electron affect the electric field?”, and unsatifsyingly, we don’t know how this happens. These things are taken as fundamental mostly because there’s no way we can come up with for us to test the mechanism underlying them, though we know there is _some_ mechanism. I don’t think it’s strictly impossible for humans to discover the answer to these questions, but we haven’t gotten there yet.
For question 2, the model has no sudden jump at the border of the object; any energy that warps spacetime warps spacetime in every direction with its influence propagating at the speed of light.
Question 3 prompts some interesting ideas- a common interpretation of general relativity is to consider all energy as moving at the speed of light through spacetime; it just happens that massive objects have most of their speed-of-light motion going through time, not space (whereas massless particles like photons move at the speed of light through space only, and don’t travel through time at all). So in effect, you’ve happened upon that interpretation yourself, and from that perspective, in some way the answer to your question 3 is yes.
@@IdeaListEye Wow, thank you so much for taking the time to answer my questions. Your answers were very helpful
@@IdeaListEye Actually, isn’t it the case that the components of massive objects are indeed moving through space at or near light speed? All of those little gluons zipping around at light speed between quarks, and quarks themselves moving at near light speed, all within the confines of protons and neutrons, are slowing time in their vicinity. The cumulative effect of a gazillion protons and neutrons in earth for example, slows time enough so that it keeps us from floating away off the surface
The collective object - a rock, our bodies - may be at rest in a Given frame of reference, but its components are moving at light speed scale
Hi! But why does the body choose the "shortest path" between the white lines? Does it have to do with minimizing the action (the length of the world line)?
Hi! Yes, as with all spontaneous actions in physics, it's a result of the system seeking the lowest energy state. Masses follow local geodesics because it requires the least amount of energy (i.e. the object would require extra energy to follow any of the non-geodesic paths; for example, a satellite in orbit is only able to maintain orbit because it has a lot of kinetic energy perpendicular to the geodesic provided by the Earth's mass).
My favorite spinning top toy as a child had a pull string, and, that thing would spin for almost a minute.